Dimmer for discharge lamps



DIMMER FOR DISCHARGE LAMPS 2 Sheets-Sheet 1 Filed Oct. 50, 1963 F I G IPR/oR ART SCRI SCRz

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PR/oR ART (0) T R A w W PRIOR ART I NVENTORS P 1965 MAMORU KURATA ETAL3,205,404

DIMMER FOR DISCHARGE LAMPS Filed Oct. 30, 1963 2 Sheets-Sheet 2 FIG.3

FIG.4

INVENTORS (WM 51% BY 95 W a W United States Patent Office 3,205,404DIMMER FOR DISCHARGE LAMPS Mamoru Kurata, Kawasaki-shi, and OsamuNomura, Tokyo, Japan, assignors to Tokyo Shibaura Electric C0., Ltd.,Kawasalri-shi, Japan, a corporation of Japan Filed Oct. 30, 1963, Ser.No. 320,013 Claims priority, application Japan, Oct. 31, 1962, 37/64,945 1 Claim. (Cl. 315194) This invention relates to a dimmer, orillumination control device for discharge lamps.

Dimmers of various types have been used for varying electric currentsupplied to electric lamp load to vary the intensity of illumination.With recent advance of semiconductor rectifiers it has been proposed touse a pair of silicon controlled rectifier elements, connected inparallel, but with opposite polarities, as the control device forvarying the current flowing through illuminating lamps. It was foundthat while such a control device operates satisfactory for ordinaryincandescent lamps, it is unable to control current flowing throughdischarge lamps because they include substantial amount of inductance inthe form of ballasts, for example.

Accordingly the object of this invention is to provide a novel dimmerfor discharge lamps.

More specific object of this invention is to provide a novel dimmercomprising a pair of reversely connected silicon controlled rectifierelements which can satisfactory control current flowing throughdischarge lamps including ballasts.

According to this invention a dimmer comprising a conduction controlleris connected between a source of al ternating current and an inductiveload including one or more discharge lamps and ballasts. The conductioncontroller incudes at least one semiconductor, such as siliconcontrolled rectifier element for varying the alternating currentsupplied to said discharge lamp or lamps. A phase shifting circuit and acramp circuit are provided to supply a gate signal of rectangular waveform to the gate electrode of the rectifier element. In this manner thewidth of the gate signal is substantially increased to assure positivetriggering of the rectifier element. By proper adjustment of the phaseshifting circuit the current supplied to the discharge lamp and henceits intensity of illumination can be varied to any desired value.

The features of the invention which are believed to be novel are setforth with particularity in the appended claims. The invention itself,however, as to its organization together with further objects andadvantages thereof may best be understood by reference to the followingdescription taken in connection with the accompanying drawings, inwhich:

FIG. 1 shows a circuit diagram of a prior dimmer for incandescent lamps;

FIG. 2 is a waveform chart wherein a, b, c and d indicate waveforms ofvarious portions of FIG. 1;

FIG. 3 shows a circuit diagram of one embodiment of this invention; and

FIG. 4 is a Waveform chart wherein a and b indicate waveforms ofportions of FIG. 3.

Referring now to the accompanying drawings, there is shown in FIG. 1 anexample of the prior art dimmer including silicon controlled rectifierelements (for the sake of simplicity, hereinafter called as rectifierelements) for controlling current flowing through incandescent lamps.Thus, in series with an incandescent lamp load R is connected to aconduction controlling device including a pair of reversely poledparallel rectifier elements SCR and SCR A suitable gate pulse generatorGP is provided to impress the control pulses across the gate and thecathode electrode of the respective rectifier element. As is well knownin the art the phase of said control pulses are varied to control thecurrent flowing;

through the rectifier elements and hence the intensity of illuminationof the incandescent lamps.

The pulse generator GP comprises, for instance, a pulse generatingcircuit including a unijunction transistor as the principal operatingelement or an equivalent circuit, said pulse generator being coupled tothe respective rectifier elements SCR and SCR through a transformerhaving a primary Winding W and two secondary windings W and W When apulse as shown in FIG. 2a is applied across the gate and cathodeelectrodes of the rectifier elements SCR and SCR these rectifierelements conduct alternately. Then the waveform of the voltage acrossthe anode and cathode electrodes will be as shown. in FIG.- 2b so thatthe voltage across the load R will be as shown in FIG. 2c- Thus, theintensity of the illumination of the lamp can be varied by changing thephase 1 of this gate control pulse over a range from zero to 1r therebyto vary the conduction period of the rectifying elements. However, inthe case of an inductive load comprising a dis-. charge lamp and aballast associated therewith, the inductance of the load operates toprevent rapid change of the load current, so that the load current cannot build up to a current level at which the rectifier elements SCR andSCR can continue conduction during the time interval from an instant Aat which the gate pulse is applied to instant B at which the pulsediminishes. Thus, it will be seen that the control device as shown inFIG. 1 can not be used as a dimmer for discharge lamps.

In accordance with this invention this defect can be obviated bysupplying a rectangular A.C. gate voltage as shown in FIG. 2d across thegate and cathode elec trodes of the respective rectifier elements inlieu of the gate pulse indicated by FIG. 2a. By using such a rectangular gate voltage having sufiicient width the controlled rectifierelements can easily attain the required conduction maintaining currentlevel.

This invention will be considered in detail by referring to FIG. 3wherein a source of alternating current A.C. is connected to a pimarywinding of a step up transformer 4 via a conduction control device 3including a pair of reversely connected controlled rectifier elements 1and 2 and a discharge lamp 6 is connected across the secondary side ofthe transformer 4 through a choke coil 5.

There is also provided a transformer 7 with its primary windingconnected across the A.C. source and the secondary windings connected tothe opposite filaments of the discharge lamp 6.

The gate signal pulse generating circuit for the controlled rectifierelements 1 and 2 comprises a phase shifting circuit including acondenser 9 and a variable resistor 10 connected in series across thesecondary winding of a transformer 8. The primary winding 13 of acoupling transformer 12 is connected through a resistor 11 between amid-tap of the secondary winding of the transformer 8 and a junctionbetween said condenser 9 and resistor 10. A pair of serially connectedZener diodes 14 and 15 of opposite polarity are connected across saidprimary winding 13. Secondary windings 16 and 17 are respectivelyconnected across the gate and cathode electrodes of said controlledrectifier elements to supply gate signal to the gates.

The operation of this invention is as follows: In the gate signalgenerating circuit, the output voltage from the phase shifting circuitcomprising the condenser 9 and the variable resistor 10 is transformedinto a square wave as shown by FIG. 4:2 by the action of the Zenerdiodes 14 and 15 and is then supplied to the primary winding 13 of thecoupling transformer 12.

Therefore, voltages induced in the secondary windings 16 and 17 andhaving similar waveform are supplied Patented Sept. 7, 1965 heavy solidline as shown in FIG. 4b. As will be clear to.

those skilled in the art, the intensity of illumination of the dischargelamp connected across the secondary winding of the transformer 4 can beadjusted to any desired value by varying the variable resistor 10. Inaccordance with this invention the gate signal supplied to thecontrolled rectifier elements 1 and 2 is not in the form of a pulse buthas substantial width by the action of the zener diode so that even whensupplying an inductive load the current flowing through the rectifierelement can attain conduction maintaining value before the gate signaldiminishes to zero, thus assuring positive control.

Thus, this invention provides a novel dimmer for a discharge lampincluding a ballast which can positively control'the current flowingthrough .suchan inductive load by applying a gate signal of rectangularwaveform generated by a phase shifting circuit and a cramp circuitacross the gate and cathode electrodes'of a semiconductor controlledrectifier element.

It will be understood, of course, that while preferred embodiments ofthis invention have been illustrated, various changes may be madewithout departingfrom the spirit of this invention and it is intended inthe appended claim to cover all such changes as'fall within the truespirit and scope of this invention.

What is claimed is:

A dimmer for a discharge lamp, comprising in combination; v

a first transformer including a primary with first end leads forconnection across an A.-C. source, conduction control means between saidend leads and said primary including a pair of rectifier elements withgate and cathode electrodes, saidrectifier elements being disposed forpassing current in opposite phase across said primary, a secondaryincluding end leads for connection to opposite filaments of a dischargelamp, and a choke coil in series with said secondary end leads and saiddischarge lamp;

a second transformer including a primary with end leads connected tosaid first end leads and two separate secondary windings each forconnection to said opposite filaments;

a third transformer having a primary with end leads connected to saidfirst end leads, a secondary with a center tap, a capacitor and avariable resistor in series with said secondary and having 'a junctionpoint therebetween;

a fourth transformerprimary connected between the center tap of saidthird transformer secondary and said junction point, apair of zenerdiodes connected in series and in opposite polarity across said fourthtransformer primary winding, and; i

a pair of fourth transformer secondary windings connected across thegateand cathode electrodes of said rectifier elements. v l

' ReferencesCited by the Examiner UNITED STATES PATENTS 3,130,347 4/64Harpley -Q. 315-400 3,158,756 11/64 I, Brunner et al.- 30788.5 3,159,76612/64, Harpley 3l5100 'JOHN W. HUCKERT, PrimaryExaminer. DAVID J.GALVIN, Examiner.

